I've read that in the "low-end" Vista versions you cannot use/access the Shadow backups, and you also cannot stop them from being created. A lot of bloggers have complained that it takes up a fair amount of disk space for an unusable feature.
The "low end" versions (non Business/Enterprise/Ultimate) do not make Shadow Copies. The feature is not installed into Windows. Not sure where that came about
(I would notice if, when I installed Crysis, suddenly 12GB went lost into space instead of 6). Disk Cleanup also says, "In some versions
of Windows Vista, the disk might include file shadow copies..."
Even the official Windows Vista website states that...
Windows Vista includes a useful innovation to help you protect your data: Shadow Copy. Available in the Ultimate, Business, and Enterprise editions of Windows Vista...
And still, even if you were using Business/Enterprise/Ultimate, you could simply go into Disk Cleanup, hit the More Options tab, and click the Clean Up button under System Restore and Shadow Copies, to clean all but the most recent restore point and all shadow copies.